S/MIME verification, marking of encryped

[Greg Troxel]

(First, thanks to everyone who has worked on gnus. I haven't updated
for a while and have been running from old git in late 2013 (because it
worked). I am trying to get S/MIME going and updated to the m0-13 tag.
I did not notice any trouble, which is great!)

I'm a longtime epg user with gnupg (coming from mailcrypt and then pgg),
and generally it works well. I am now trying to get set up with S/MIME
to interact with some people who do encrypted mail that way, and finding
it harder than it seems I should.

Part of my problem is the mysterious "No CA configured" error. That
seems to come from smime.el, but I've tried to configure the use of epg
and thus gpgsm, and that seems to actually work.

Specific questions:

0) I put in .emacs:

(setq mml-smime-use 'epg)

Is that sufficient and appropriate to make gnus use epg/gpgsm for
S/MIME?

1) What is the thinking on the default for smime between epg/gpgsm and
openssl? It seems to me that gpgsm is set up for passphrases and also
to mark keys/CAs trusted or not in a more flexible manner, so that seems
preferred. But Simon wrote smime.el, so I don't want to jump to
conclusions.

2) Are people sure that there are no control flow leaks into the openssl
code when epg is configured? I am set up for gpgsm, and verifying
messages that are from myself and signed or signed and encrypted seems
to work. Verifying a message that is encrypted but not signed from
someone else gives the "No CA configured" error. However, while doing
this, I see that gpgsm was run and openssl was not (from atimes on the
binaries).

3) When verifying openpgp/mime, I am notified of decryption status as
well as signatures, so that I know the message was encrypted. I don't
see any hint of this with epg/gpgsm. Any advice, other than figure it
out and send a patch?

Thanks,
Greg

[j***@fsfe.org]

Hi Greg!

Post by Greg Troxel
I'm a longtime epg user with gnupg (coming from mailcrypt and then
pgg), and generally it works well. I am now trying to get set up with
S/MIME to interact with some people who do encrypted mail that way,
and finding it harder than it seems I should.

If I understand correctly, they already use S/MIME, right? So, probably
this choice is not yours to make, but I recommend OpenPGP over S/MIME,
as explained in a blog entry:
https://blogs.fsfe.org/jens.lechtenboerger/2013/12/23/openpgp-and-smime/

Post by Greg Troxel
Part of my problem is the mysterious "No CA configured" error. That
seems to come from smime.el, but I've tried to configure the use of
epg and thus gpgsm, and that seems to actually work.

If you get that error you can be certain that openssl code was involved,
which is a bug.

Post by Greg Troxel
(setq mml-smime-use 'epg)
Is that sufficient and appropriate to make gnus use epg/gpgsm for
S/MIME?

That should do it. Alternatively, you could put
(require 'epg)
into .emacs (early on, before other encryption-related code gets called).

Post by Greg Troxel
1) What is the thinking on the default for smime between epg/gpgsm and
openssl?

My recommendation is to stay away from openssl. Use gpgsm.

Post by Greg Troxel
It seems to me that gpgsm is set up for passphrases and also
to mark keys/CAs trusted or not in a more flexible manner, so that
seems preferred. But Simon wrote smime.el, so I don't want to jump to
conclusions.

In general, gpgsm includes full-fledged certificate management, which
you need to perform manually with openssl (storage, expiry, revocation).
Then, depending of your version of openssl you may be advertising broken
encryption algorithms (in your signatures). Also, you may want to read
the BUGS section of man smime(1) and man cms(1). In the blog entry
mentioned above, these points are explained with some Emacs specific
additions.

Post by Greg Troxel
2) Are people sure that there are no control flow leaks into the
openssl code when epg is configured? I am set up for gpgsm, and
verifying messages that are from myself and signed or signed and
encrypted seems to work. Verifying a message that is encrypted but
not signed from someone else gives the "No CA configured" error.
However, while doing this, I see that gpgsm was run and openssl was
not (from atimes on the binaries).

No, there is at least one open bug: mm-view-pkcs7-verify is hard-wired
for openssl, while mm-view-pkcs7-decrypt respects mml-smime-use.
https://debbugs.gnu.org/cgi/bugreport.cgi?bug=18393

Post by Greg Troxel
3) When verifying openpgp/mime, I am notified of decryption status as
well as signatures, so that I know the message was encrypted. I don't
see any hint of this with epg/gpgsm. Any advice, other than figure it
out and send a patch?

For signed plaintext messages I see the verification status. For signed
and encrypted ones not. My advice is to go for OpenPGP :-)

Best wishes
Jens

[Greg Troxel]

Post by j***@fsfe.org
Hi Greg!

Post by Greg Troxel
I'm a longtime epg user with gnupg (coming from mailcrypt and then
pgg), and generally it works well. I am now trying to get set up with
S/MIME to interact with some people who do encrypted mail that way,
and finding it harder than it seems I should.

If I understand correctly, they already use S/MIME, right? So, probably
this choice is not yours to make, but I recommend OpenPGP over S/MIME,
https://blogs.fsfe.org/jens.lechtenboerger/2013/12/23/openpgp-and-smime/

You will notice that my messages to this list are signed with OpenPGP.
Indeed my question is about how to interoperate with people that already
use S/MIME.

Your blog post conflates the common PKI model and the S/MIME standard
itself - which I realize is how normal people come to this. Some
organizations use S/MIME but only configure their own CAs as trust
anchors. This is quite sane. But I agree that that vast CA list is
goofy and inflicted on most people.

Post by j***@fsfe.org

Post by Greg Troxel
1) What is the thinking on the default for smime between epg/gpgsm and
openssl?

My recommendation is to stay away from openssl. Use gpgsm.

So perhaps the defaults should be flipped in gnus, so that epg/gpgsm is
used, throwing an error if not found (or silently not decoding merely
signed?), unless someone has explicitly asked for the openssl version?

Post by j***@fsfe.org

Post by Greg Troxel
3) When verifying openpgp/mime, I am notified of decryption status as
well as signatures, so that I know the message was encrypted. I don't
see any hint of this with epg/gpgsm. Any advice, other than figure it
out and send a patch?

For signed plaintext messages I see the verification status. For signed
and encrypted ones not. My advice is to go for OpenPGP :-)

You vastly overestimate my status as world dictator :-)

[j***@fsfe.org]

Post by Greg Troxel
Your blog post conflates the common PKI model and the S/MIME standard
itself

I hope not. I explain that you need a notion of trust, and I also
mention the case of the monopoly.

Post by Greg Troxel
- which I realize is how normal people come to this.

Come to what?

Post by Greg Troxel
Some organizations use S/MIME but only configure their own CAs as
trust anchors. This is quite sane. But I agree that that vast CA
list is goofy and inflicted on most people.

Using just your own CA conflicts with the decentralized model of e-mail.

Post by Greg Troxel

Post by j***@fsfe.org
My recommendation is to stay away from openssl. Use gpgsm.

So perhaps the defaults should be flipped in gnus, so that epg/gpgsm is
used, throwing an error if not found (or silently not decoding merely
signed?), unless someone has explicitly asked for the openssl version?

Yes, I agree. Actually, I plan to propose that later this month.
Currently, I’m working on the refactoring of encryption related code in
Gnus that I proposed more than a year ago on this list.

Post by Greg Troxel

Post by j***@fsfe.org
My advice is to go for OpenPGP :-)

You vastly overestimate my status as world dictator :-)

Too bad. Definitely worth a try.

Best wishes
Jens

[Greg Troxel]

Post by j***@fsfe.org

Post by Greg Troxel

Post by j***@fsfe.org
My recommendation is to stay away from openssl. Use gpgsm.

So perhaps the defaults should be flipped in gnus, so that epg/gpgsm is
used, throwing an error if not found (or silently not decoding merely
signed?), unless someone has explicitly asked for the openssl version?

Yes, I agree. Actually, I plan to propose that later this month.
Currently, I’m working on the refactoring of encryption related code in
Gnus that I proposed more than a year ago on this list.

I look forward to testing this.

Following up on some previous discussion:

In theory an S/MIME implementation could allow for flexible
user-controlled key management, where one could choose to trust an
end-user cert without enabling a CA. But having tried this with
Mail.app and gpgsm, I find that you are entirely right and that the
standard PKI model is very baked in. With gpgsm this is about just
mail, but with Mail.app it gets into "do you want to trust random
company's CA for x.509 certs in general".

Thanks for the advice about this.

Greg

[Uwe Brauer]

Post by j***@fsfe.org
Hi Greg!
If I understand correctly, they already use S/MIME, right? So, probably
this choice is not yours to make, but I recommend OpenPGP over S/MIME,
https://blogs.fsfe.org/jens.lechtenboerger/2013/12/23/openpgp-and-smime/

I disagree. Smime is much easier for most users to use. Using a maybe
technical superior solution but having nobody to communicate with is a
mayor drawback.

Post by j***@fsfe.org
If you get that error you can be certain that openssl code was involved,
which is a bug.
That should do it. Alternatively, you could put
(require 'epg)
into .emacs (early on, before other encryption-related code gets called).
My recommendation is to stay away from openssl. Use gpgsm.

I agree I never got openssl to work while gpgsm works without any
problems.
If you like I can send my private setting off list

Uwe Brauer